Sun Revenge!

Retaliate is not only STAB but it gets double power if used right after another one of your Pokemon is fainted! Coming of a 328 Attack stat further boosted either to 492 (By Choice-band) or 426 (By Life-orb) will destroy almost anything that is not immune/resistant to it. Horn-leech is STAB and healing, very good especially with Life-orb as it heals off the damage. Nature-power becomes Earthquake in Wi-fi and PO (Pokemon Online) so it is an obvious choice for coverage. Mega-horn or Wild-charge choose your coverage. His speed is 557 with Chlorophyll boost which allows you to outspeed anything that is not boosted, but if you really fear scarfed Pokemon you can put full EVs into speed.

Revenge killer.
Sap Sipper lets him take in Grass moves for teammates, boosting that attack.
Or, bring this guy out after one of you other Pokemon has fainted. STAB, double power, and Life Orb will hurt.
Nature Power becomes Earthquake, give Fire type coverage.
Megahorn covers annoying Psychics, or Jump Kick to get Fighting type coverage.
Horn Leech is STAb and recovers Life Orb damage.

Sawsbuck is a good choice I honestly think, despite the numerous weaknesses.
Ability: sap sipper (do not waste your time and effort with chlorophyll)
moveset:
Double Edge: good strong attack with STAB
Sword Dance: sets up some good sweeper opportunities
Baton Pass: obviously to pass on your sword dance
Horn Leech: Heals Sawsbuck and makes up for the lost hp that you would have lost after using double edge and sword dance (if the opponent used an attack)